1. Field of the Invention
The present invention relates to microscopes and darkfield objectives, and in particular, relates to microscopes and darkfield objectives that perform reflected darkfield illumination.
2. Description of the Related Art
Illumination methods that are adopted in conventional general microscopes for reflected darkfield observation fall into two broad categories.
In the first method, darkfield illumination is performed by using the light from a light source of a microscope main body, which is used for brightfield observation. Typically, the light from a light source of a microscope main body is reflected by hollow mirrors that are arranged in the microscope main body, and a circular luminous flux that enters the darkfield illumination optical path in a darkfield objective is formed. Moreover, it is usually the case that incident end of the darkfield illumination optical path in a darkfield objective is arranged inside the screw unit for fitting a darkfield objective to the microscope main body.
In the second method, darkfield illumination is performed by using the light from a light source that is provided for a darkfield objective. Typically, the emission end of a fiber light source or LEDs are circularly arranged outside the lens system of a darkfield objective, and a circular luminous flux is formed.
In recent years, there has been increasing demand for greater numerical apertures and greater working distances, and there has been a growing trend for a greater outside diameter of a lens system that constitutes an objective. Accordingly, the outside diameter of a darkfield illumination optical path that is formed outside the lens system is also increasing.
In regard to the above point, when the first method is adopted, the luminous flux diameter in the microscope main body may be thickened according to the upsizing of the outside diameter of a darkfield illumination optical path that is formed in this objective. However, the configuration in which a luminous flux with a thick diameter passes through a microscope main body causes a lot of disadvantages, such as the upsizing of an optical system in a microscope main body and arrangement restrictions. For this reason, as disclosed, for example, in Japanese Laid-open Patent Publication No. 2012-013879 and Japanese Examined Patent Application Publication No. 04-048203, a method in which a luminous flux with a conventional diameter is emitted from a microscope main body so as to enter an objective and the luminous flux diameter is enlarged inside the objective has been proposed.
On the other hand, when the second method in which a light source is arranged outside the lens system is adopted, no special action is required for the upsizing of a lens system that constitutes an objective. The second method is disclosed, for example, in Japanese Laid-open Patent Publication No. 2009-063856 and Japanese Laid-open Patent Publication No. 02-097909.